NMULF and NMULD are efficient FP instructions, and the go compiler can
use them to generate better code.

The benchmark tests of my patch did not show general change, but big
improvement in special cases.

1.A special test case improved 12.6%.
https://github.com/benshi001/ugo1/blob/master/fpmul_test.go
name                     old time/op    new time/op    delta
FPMul-4                     398µs ± 1%     348µs ± 1%  -12.64%  (p=0.000 n=40+40)

2. the compilecmp test showed little change.
name        old time/op       new time/op       delta
Template          2.30s ± 1%        2.31s ± 1%    ~     (p=0.754 n=17+19)
Unicode           1.31s ± 3%        1.32s ± 5%    ~     (p=0.265 n=20+20)
GoTypes           7.73s ± 2%        7.73s ± 1%    ~     (p=0.925 n=20+20)
Compiler          37.0s ± 1%        37.3s ± 2%  +0.79%  (p=0.002 n=19+20)
SSA               83.8s ± 4%        83.5s ± 2%    ~     (p=0.964 n=20+17)
Flate             1.43s ± 2%        1.44s ± 1%    ~     (p=0.602 n=20+20)
GoParser          1.82s ± 2%        1.81s ± 2%    ~     (p=0.141 n=19+20)
Reflect           5.08s ± 2%        5.08s ± 3%    ~     (p=0.835 n=20+19)
Tar               2.36s ± 1%        2.35s ± 1%    ~     (p=0.195 n=18+17)
XML               2.57s ± 2%        2.56s ± 1%    ~     (p=0.283 n=20+17)
[Geo mean]        4.74s             4.75s       +0.05%

name        old user-time/op  new user-time/op  delta
Template          2.75s ± 2%        2.75s ± 0%    ~     (p=0.620 n=20+15)
Unicode           1.59s ± 4%        1.60s ± 4%    ~     (p=0.479 n=20+19)
GoTypes           9.48s ± 1%        9.47s ± 1%    ~     (p=0.743 n=20+20)
Compiler          45.7s ± 1%        45.7s ± 1%    ~     (p=0.482 n=19+20)
SSA                109s ± 1%         109s ± 2%    ~     (p=0.800 n=18+20)
Flate             1.67s ± 3%        1.67s ± 3%    ~     (p=0.598 n=19+18)
GoParser          2.15s ± 4%        2.13s ± 3%    ~     (p=0.153 n=20+20)
Reflect           5.95s ± 2%        5.95s ± 2%    ~     (p=0.961 n=19+20)
Tar               2.93s ± 2%        2.92s ± 3%    ~     (p=0.242 n=20+19)
XML               3.02s ± 3%        3.04s ± 3%    ~     (p=0.233 n=19+18)
[Geo mean]        5.74s             5.74s       -0.04%

name        old text-bytes    new text-bytes    delta
HelloSize         588kB ± 0%        588kB ± 0%    ~     (all equal)

name        old data-bytes    new data-bytes    delta
HelloSize        5.46kB ± 0%       5.46kB ± 0%    ~     (all equal)

name        old bss-bytes     new bss-bytes     delta
HelloSize        72.9kB ± 0%       72.9kB ± 0%    ~     (all equal)

name        old exe-bytes     new exe-bytes     delta
HelloSize        1.03MB ± 0%       1.03MB ± 0%    ~     (all equal)

3. The go1 benchmark showed little change in total.
name                     old time/op    new time/op    delta
BinaryTree17-4              41.8s ± 1%     41.8s ± 1%    ~     (p=0.388 n=40+39)
Fannkuch11-4                24.1s ± 1%     24.1s ± 1%    ~     (p=0.077 n=40+40)
FmtFprintfEmpty-4           834ns ± 1%     831ns ± 1%  -0.31%  (p=0.002 n=40+37)
FmtFprintfString-4         1.34µs ± 1%    1.34µs ± 0%    ~     (p=0.387 n=40+40)
FmtFprintfInt-4            1.44µs ± 1%    1.44µs ± 1%    ~     (p=0.421 n=40+40)
FmtFprintfIntInt-4         2.09µs ± 0%    2.09µs ± 1%    ~     (p=0.589 n=40+39)
FmtFprintfPrefixedInt-4    2.32µs ± 1%    2.33µs ± 1%  +0.15%  (p=0.001 n=40+40)
FmtFprintfFloat-4          4.51µs ± 0%    4.44µs ± 1%  -1.50%  (p=0.000 n=40+40)
FmtManyArgs-4              7.94µs ± 0%    7.97µs ± 0%  +0.36%  (p=0.001 n=32+40)
GobDecode-4                 104ms ± 1%     102ms ± 2%  -1.27%  (p=0.000 n=39+37)
GobEncode-4                90.5ms ± 1%    90.9ms ± 2%  +0.40%  (p=0.006 n=37+40)
Gzip-4                      4.10s ± 2%     4.08s ± 1%  -0.30%  (p=0.004 n=40+40)
Gunzip-4                    603ms ± 0%     602ms ± 1%    ~     (p=0.303 n=37+40)
HTTPClientServer-4          672µs ± 3%     658µs ± 2%  -2.08%  (p=0.000 n=39+37)
JSONEncode-4                238ms ± 1%     239ms ± 0%  +0.26%  (p=0.001 n=40+25)
JSONDecode-4                884ms ± 1%     885ms ± 1%  +0.16%  (p=0.012 n=40+40)
Mandelbrot200-4            49.3ms ± 0%    49.3ms ± 0%    ~     (p=0.588 n=40+38)
GoParse-4                  46.3ms ± 1%    46.4ms ± 2%    ~     (p=0.487 n=40+40)
RegexpMatchEasy0_32-4      1.28µs ± 1%    1.28µs ± 0%  +0.12%  (p=0.003 n=40+40)
RegexpMatchEasy0_1K-4      7.78µs ± 5%    7.78µs ± 4%    ~     (p=0.825 n=40+40)
RegexpMatchEasy1_32-4      1.29µs ± 1%    1.29µs ± 0%    ~     (p=0.659 n=40+40)
RegexpMatchEasy1_1K-4      10.3µs ± 3%    10.4µs ± 2%    ~     (p=0.266 n=40+40)
RegexpMatchMedium_32-4     2.05µs ± 1%    2.05µs ± 0%  -0.18%  (p=0.002 n=40+28)
RegexpMatchMedium_1K-4      533µs ± 1%     534µs ± 1%    ~     (p=0.397 n=37+40)
RegexpMatchHard_32-4       28.9µs ± 1%    28.9µs ± 1%  -0.22%  (p=0.002 n=40+40)
RegexpMatchHard_1K-4        868µs ± 1%     870µs ± 1%  +0.21%  (p=0.015 n=40+40)
Revcomp-4                  67.3ms ± 1%    67.2ms ± 2%    ~     (p=0.262 n=38+39)
Template-4                  1.07s ± 1%     1.07s ± 1%    ~     (p=0.276 n=40+40)
TimeParse-4                7.16µs ± 1%    7.16µs ± 1%    ~     (p=0.610 n=39+40)
TimeFormat-4               13.3µs ± 1%    13.3µs ± 1%    ~     (p=0.617 n=38+40)
[Geo mean]                  720µs          719µs       -0.13%

name                     old speed      new speed      delta
GobDecode-4              7.39MB/s ± 1%  7.49MB/s ± 2%  +1.25%  (p=0.000 n=39+38)
GobEncode-4              8.48MB/s ± 1%  8.45MB/s ± 2%  -0.40%  (p=0.005 n=37+40)
Gzip-4                   4.74MB/s ± 2%  4.75MB/s ± 1%  +0.30%  (p=0.018 n=40+40)
Gunzip-4                 32.2MB/s ± 0%  32.2MB/s ± 1%    ~     (p=0.272 n=36+40)
JSONEncode-4             8.15MB/s ± 1%  8.13MB/s ± 0%  -0.26%  (p=0.003 n=40+25)
JSONDecode-4             2.19MB/s ± 1%  2.19MB/s ± 1%    ~     (p=0.676 n=40+40)
GoParse-4                1.25MB/s ± 2%  1.25MB/s ± 2%    ~     (p=0.823 n=40+40)
RegexpMatchEasy0_32-4    25.1MB/s ± 1%  25.1MB/s ± 0%  -0.12%  (p=0.006 n=40+40)
RegexpMatchEasy0_1K-4     132MB/s ± 5%   132MB/s ± 5%    ~     (p=0.821 n=40+40)
RegexpMatchEasy1_32-4    24.7MB/s ± 1%  24.7MB/s ± 0%    ~     (p=0.630 n=40+40)
RegexpMatchEasy1_1K-4    99.1MB/s ± 3%  98.8MB/s ± 2%    ~     (p=0.268 n=40+40)
RegexpMatchMedium_32-4    487kB/s ± 2%   490kB/s ± 0%  +0.51%  (p=0.001 n=40+40)
RegexpMatchMedium_1K-4   1.92MB/s ± 1%  1.92MB/s ± 1%    ~     (p=0.208 n=39+40)
RegexpMatchHard_32-4     1.11MB/s ± 1%  1.11MB/s ± 0%  +0.36%  (p=0.000 n=40+33)
RegexpMatchHard_1K-4     1.18MB/s ± 1%  1.18MB/s ± 1%    ~     (p=0.207 n=40+37)
Revcomp-4                37.8MB/s ± 1%  37.8MB/s ± 2%    ~     (p=0.276 n=38+39)
Template-4               1.82MB/s ± 1%  1.81MB/s ± 1%    ~     (p=0.122 n=38+40)
[Geo mean]               6.81MB/s       6.81MB/s       +0.06%

fixes #19843

Change-Id: Ief3a0c2b15f59d40c7b40f2784eeb71196685b59
Reviewed-on: https://go-review.googlesource.com/61150Reviewed-by: Cherry Zhang <cherryyz@google.com>
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>